1. Field of the Invention
The present invention relates to a communication device including a plurality of communication systems, particularly a communication device including a plurality of communication systems utilizing an UHF band.
2. Description of the Related Art
An example of a radio device used in a RFID (Radio Frequency Identification) system is disclosed in WO 2009/011154. According to the background art, a radio IC chip processing transmission and reception signals for RFID is mounted on a printed circuit board. The printed circuit board also includes a ground electrode and a loop electrode. The loop electrode is electrically conducted with the radio IC chip, and is connected with the ground electrode by electromagnetic coupling or directly in a DC-connected manner. The radio frequency signal received by the ground electrode is input to the radio IC chip through the loop electrode, whereas the radio frequency signal output from the radio IC chip is emitted outside from the ground electrode through the loop electrode. In other words, the ground electrode functions as a radiating element in the RFID system.
However, in the case where a radio communication system transmitting and receiving another radio frequency signal such as a GSM (Global System for Mobile Communications: registered trademark) system is additionally mounted on the printed circuit board, particularly in the case where the frequency band corresponding to each of different radio communication systems such as the RFID system and the GSM system is in common, the radio frequency signal of high intensity transmitted by the radio communication system will be distorted by the radio IC chip for the RFID system, and the harmonic wave component generated thereby may be emitted from the ground electrode or the antenna element for the GSM system as a spurious response.
In other words, in a communication system mounted with a first radio communication system such as the RFID system and also a second radio communication system such as the GSM system, the communication performance will be degraded by the generation of the aforementioned harmonic wave component and radiation thereof.